arXiv subjects

Javier Fuentes-Martin

Publications and source records attributed to Javier Fuentes-Martin.

28 records · Page 2Linked to original sources

arXiv2017

DsixTools: The Standard Model Effective Field Theory Toolkit

We present DsixTools, a Mathematica package for the handling of the dimension-six Standard Model Effective Field Theory. Among other features, DsixTools allows the user to perform the full one-loop Renormalization Group Evolution of the Wilson coefficients in the Warsaw basis. This is achieved thanks to the SMEFTrunner module, which implements the full one-loop anomalous dimension matrix previously derived in the literature. In addition, DsixTools also contains modules devoted to the matching to the $ΔB = ΔS = 1,2$ and $ΔB = ΔC = 1$ operators of the Weak Effective Theory at the electroweak scale and their QCD and QED Renormalization Group Evolution below the electroweak scale.

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arXiv2017

Lepton Flavor Non-Universality in B decays from Dynamical Yukawas

The basic features of quark and lepton mass matrices can be successfully explained by natural minima of a generic potential with dynamical Yukawa fields invariant under the $[\mathrm{SU(3)}]^5\times \mathcal{O}(3)$ flavor symmetry. If this symmetry is gauged, in order to avoid potentially dangerous Goldstone bosons, and small perturbations are added to exactly fit the observed pattern of fermion masses, the spectrum of massive flavor gauge bosons can naturally explain the hints for new physics in $b\to s \ell^+\ell^-$ transitions, including $R_K$. In particular, the desired pattern of the Standard Model Yukawa couplings is compatible with a gauged $\mathrm{U(1)}_q$ in the quark sector, and $\mathrm{U(1)}_{μ-τ}$ in the lepton sector spontaneously broken around the TeV scale. In order to explain the aforementioned experimental hints, the corresponding neutral gauge bosons are required to mix, yielding to potentially observable signals in dimuon resonance searches at the LHC.

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arXiv2016

Phenomenology of an $SU(2) \times SU(2) \times U(1)$ model with lepton-flavour non-universality

We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in $b \to c \ell ν$ and $b \to s \ell^+ \ell^-$ decays at BaBar, Belle and LHCb. The model consists of an extended gauge group $\mathrm{SU(2)}_{1} \times \mathrm{SU(2)}_{2} \times \mathrm{U(1)}_Y$ which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector-like fermions give rise to potentially large new physics contributions in flavour transitions mediated by $W^{\prime}$ and $Z^{\prime}$ bosons. This model can ease tensions in $B$-physics data while satisfying stringent bounds from flavour physics, tau decays, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the lepton flavour violating ratios $R_M$, with $M = K^*, ϕ$, are found to be reduced with respect to the Standard Model expectation $R_M \simeq 1$.

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arXiv2016

Integrating out heavy particles with functional methods: a simplified framework

We present a systematic procedure to obtain the one-loop low-energy effective Lagrangian resulting from integrating out the heavy fields of a given ultraviolet theory. We show that the matching coefficients are determined entirely by the hard region of the functional determinant involving the heavy fields. This represents an important simplification with respect the conventional matching approach, where the full and effective theory contributions have to be computed separately and a cancellation of the infrared divergent parts has to take place. We illustrate the method with a descriptive toy model and with an extension of the Standard Model with a heavy real scalar triplet. A comparison with other schemes that have been put forward recently is also provided.

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arXiv2016

Non-abelian gauge extensions for B-decay anomalies

We study the generic features of minimal gauge extensions of the Standard Model in view of recent hints of lepton-flavor non-universality in semi-leptonic $b \to s \ell^+ \ell^-$ and $b \to c \ell ν$ decays. We classify the possible models according to the symmetry-breaking pattern and the source of flavor non-universality. We find that in viable models the $\mathrm{SU(2)}_L$ factor is embedded non-trivially in the extended gauge group, and that gauge couplings should be universal, hinting to the presence of new degrees of freedom sourcing non-universality. Finally, we provide an explicit model that can explain the $B$-decay anomalies in a coherent way and confront it with the relevant phenomenological constraints.

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arXiv2015

A class of Z' models with non-universal couplings and protected flavor-changing interactions

Motivated by the $b\to s\ell^+\ell^-$ anomalies recently reported by the LHCb collaboration, I present a class of flavored U(1)' gauge extensions of the Standard Model that naturally accommodates them and possesses a rich phenomenology. This model is characterized by the presence of tree-level flavor-changing interactions in the down-quark sector, protected by off-diagonal quark-mixing matrix elements. Anomaly cancellation fixes the extension of the symmetry to the lepton sector in a very specific way, giving rise to flavor-conserving family-non-universal Z' couplings. The fermion content of this model is the same as in the SM while the scalar sector is extended with an extra Higgs doublet and a scalar singlet. The model will be tested in the next run of LHC and presents specific correlations in certain flavor observables that allow to clearly discriminate among them and from other new physics signals.

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arXiv2015

Family non-universal Z' models with protected flavor-changing interactions

We define a new class of $Z'$ models with neutral flavor-changing interactions at tree level in the down-quark sector. They are related in an exact way to elements of the quark mixing matrix due to an underlying flavored $U(1)'$ gauge symmetry, rendering these models particularly predictive. The same symmetry implies lepton-flavor non-universal couplings, fully determined by the gauge structure of the model. Our models allow to address presently observed deviations from the SM and specific correlations among the new physics contributions to the Wilson coefficients $C_{9,10}^{(\prime) \ell}$ can be tested in $b \to s \ell^+ \ell^-$ transitions. We furthermore predict lepton-universality violations in $Z'$ decays, testable at the LHC.

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arXiv2015

A class of invisible axion models with FCNCs at tree level

We build a class of invisible axion models with tree-level Flavor Changing Neutral Currents completely controlled by the fermion mixing matrices. The scalar sector of these models contains three-Higgs doublets and a complex scalar gauge singlet, with the same fermionic content than the Standard Model. A horizontal Peccei-Quinn symmetry provides a solution to the strong CP problem and predicts the existence of a very light and weakly coupled pseudo-Goldstone boson, the invisible axion or familon. A phenomenological analysis is performed taking into account familon searches in rare kaon and muon decays, astrophysical considerations and axion searches via axion-photon conversion. Drastic differences are found in the axion properties of different models due to the strong hierarchy of the CKM matrix, making some of the models considered much more constrained than others. We also obtain that a rich variety of these models avoid the domain wall problem. A possible mechanism to protect the solution to the strong CP problem against gravitational effects is also discussed.

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arXiv2015

An invisible axion model with controlled FCNCs at tree level

We derive the necessary conditions to build a class of invisible axion models with Flavor Changing Neutral Currents at tree-level controlled by the fermion mixing matrices and present an explicit model implementation. A horizontal Peccei-Quinn symmetry provides a solution to the strong CP problem via the Peccei-Quinn mechanism and predicts a cold dark mater candidate, the invisible axion or familon. The smallness of active neutrino masses can be explained via a type I seesaw mechanism, providing a dynamical origin for the heavy seesaw scale. The possibility to avoid the domain wall problem stands as one of the most interesting features of the type of models considered. Experimental limits relying on the axion-photon coupling, astrophysical considerations and familon searches in rare kaon and muon decays are discussed.

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arXiv2014

Effective Aligned 2HDM with a DFSZ-like invisible axion

We discuss the possibility of having a non-minimal scalar sector at the weak scale within the framework of invisible axion models. To frame our discussion we consider an extension of the Dine-Fischler-Srednicki-Zhitnitsky invisible axion model with two additional Higgs doublets blind under the Peccei-Quinn symmetry. Due to mixing effects among the scalar fields, it is possible to obtain a rich scalar sector at the weak scale in certain decoupling limits of the theory. In particular, this framework provides an ultraviolet completion of the so-called aligned two-Higgs-doublet model and solves the strong CP problem. The axion properties and the smallness of active neutrino masses are also discussed.

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